Roles of the Ras/Raf/MEK/ERK pathway in leukemia therapy.

The Ras/Raf/mitogen-activated protein kinase (MEK)/extracellular signal-regulated kinase (ERK) pathway is often implicated in sensitivity and resistance to leukemia therapy. Dysregulated signaling through the Ras/Raf/MEK/ERK pathway is often the result of genetic alterations in critical components in this pathway as well as mutations at upstream growth factor receptors. Unrestricted leukemia proliferation and decreased sensitivity to apoptotic-inducing agents and chemoresistance are typically associated with activation of pro-survival pathways. Mutations in this pathway and upstream signaling molecules can alter sensitivity to small molecule inhibitors targeting components of this cascade as well as to inhibitors targeting other key pathways (for example, phosphatidylinositol 3 kinase (PI3K)/phosphatase and tensin homologue deleted on chromosome 10 (PTEN)/Akt/mammalian target of rapamycin (mTOR)) activated in leukemia. Similarly, PI3K mutations can result in resistance to inhibitors targeting the Ras/Raf/MEK/ERK pathway, indicating important interaction points between the pathways (cross-talk). Furthermore, the Ras/Raf/MEK/ERK pathway can be activated by chemotherapeutic drugs commonly used in leukemia therapy. This review discusses the mechanisms by which abnormal expression of the Ras/Raf/MEK/ERK pathway can contribute to drug resistance as well as resistance to targeted leukemia therapy. Controlling the expression of this pathway could improve leukemia therapy and ameliorate human health.

Targeting the translational apparatus to improve leukemia therapy: roles of the PI3K/PTEN/Akt/mTOR pathway.

It has become apparent that regulation of protein translation is an important determinant in controlling cell growth and leukemic transformation. The phosphoinositide 3-kinase (PI3K)/phosphatase and tensin homologue deleted on chromosome ten (PTEN)/Akt/mammalian target of rapamycin (mTOR) pathway is often implicated in sensitivity and resistance to therapy. Dysregulated signaling through the PI3K/PTEN/Akt/mTOR pathway is often the result of genetic alterations in critical components in this pathway as well as mutations at upstream growth factor receptors. Furthermore, this pathway is activated by autocrine transformation mechanisms. PTEN is a critical tumor suppressor gene and its dysregulation results in the activation of Akt. PTEN is often mutated, silenced and is often haploinsufficient. The mTOR complex1 (mTORC1) regulates the assembly of the eukaryotic initiation factor4F complex, which is critical for the translation of mRNAs that are important for cell growth, prevention of apoptosis and transformation. These mRNAs have long 5'-untranslated regions that are G+C rich, rendering them difficult to translate. Elevated mTORC1 activity promotes the translation of these mRNAs via the phosphorylation of 4E-BP1. mTORC1 is a target of rapamycin and novel active-site inhibitors that directly target the TOR kinase activity. Although rapamycin and novel rapalogs are usually cytostatic and not cytotoxic for leukemic cells, novel inhibitors that target the kinase activities of PI3K and mTOR may prove more effective for leukemia therapy.

Laser tweezers Raman spectroscopy potential for studies of complex dynamic cellular processes: single cell bacterial lysis.

The potential of laser tweezers Raman spectroscopy (LTRS) to study complex and dynamic cellular processes was investigated on the model of single E. coli cells lysed (1) from "outside" with egg white lysozyme and (2) from "within" by temperature-induced temperate bacteriophage lambdacI857. The two lysis processes differed in the final outcome (incomplete vs complete cell lysis) as revealed by the dynamic laser light scattering and exhibited distinctive dynamic Raman spectra changes. The technique enabled for the first time at the cellular level to observe and quantify real time interaction of lysozyme with E. coli cells, "visualize" a side effect of the process due to the presence of EDTA, and correlate the process of cell wall disruption, as evidenced by the onset and development of asymmetric speckle scattering patterns, with release/escape of intracellular material (ribosomes, nucleic acids, proteins, etc.) quantified by the intensity changes of Raman signatures. Raman spectra changes observed during the lysis from "within" suggest alleged production of heat shock proteins are consistent with the occurring synthesis of phage-related proteins and are in good agreement with the calculated potential contribution of the above proteins to the Raman spectra. It was also established and validated that the contribution of cellular DNA to the Raman spectra of bacterial cells is negligible compared to RNA. The results open new venues for LTRS research and strongly suggest that LTRS has a great potential especially in investigation of real-time processes.